Forehead scar revision didn't work. What else can I do?

First, let me say how sorry I am that you are suffering so from this problem. While a scar unfortunately cannot be completely removed with any existing technology, happily it can often be improved dramatically. A linear indented scar may be elevated by subcision, either alone or in combination with the use of a lifting filler, such as Restylane Lyft (which would be my choice in my Upper East Side Manhattan practice or Hyaluronica 2, my go-to for this in my Israel satellite facility where a far greater number of regulatory agency approved fillers and volumizers are available). Fractional microneedle resurfacing (aka medical microneedling, skin needling, dermal rolling) may then be employed afterward, if necessary,  following subcision, to further blend the tone and texture of the treated scar with that of the surrounding normal skin. For more information on any of the above, check out the archives of RealSelf.com, and be sure to seek consultation with a board certified aesthetic physician. 

This can be improved with lasers subcision and fillers. I suggest seeing a cosmetic dermatologist with experience.  Best, Dr. Emer.

Hi AM.  It appears that you have two options (besides another surgery) - laser resurfacing and subcision with injections.  Laser resurfacing can help with contoured scars like the one shown but results are variable.  It's not going to eliminate the scar, but rather improve it.The other option is subcision which aims to break up scar tissue below indented scars with the needle that is used to inject Restylane or Perlane.  This is meant to decrease the size of the indentation.  For photos of scar revision procedures, click on the link below.  

From looking at your picture the actual scar looks to have healed very well.  The scar is flat and without color.  The underlying concavity (if that is what bothers you) can be filled with fat or filler to improve the contour.